Figure 13.8.
(A) Fluorescence titrations of the 40-mer, dεA(pεA)39, with the PriA protein (λex = 325 nm, λem = 410 nm) in buffer C (pH 7.0, 10 °C), containing 100 mM NaCl, at two different nucleic acid concentrations: (■) 4.6 × 10−7 M; (□) 4 × 10−6 M. The solid lines are nonlinear least-squares fits of the titration curves, using the statistical thermodynamic model for the binding of two PriA molecules to the 40-mer, described by Eqs. (13.14)–(13.17). The intrinsic binding constant Kp = 5.6 × 104 M−1, cooperativity parameter ω = 0.8, and relative fluorescence change ΔF1 = 1.7, and ΔFmax = 3.5, respectively. (B) Dependence of the relative fluorescence of the 40-mer, ΔFobs, upon the total average degree of binding of the PriA proteins, ΣΘi (■). The solid line follows the experimental points and has no theoretical basis. The dashed line is the extrapolation of ΔFobs to the maximum value of ΔFmax = 3.5.